Journal articles on the topic 'Fault zones – Maine'

Three deep-penetration seismic reflection profiles were collected off southwest Nova Scotia to determine the crustal structure and geometry beneath the Avalon and Meguma zones of the Appalachian Orogen in Canada. Onshore geological features have been traced seawards using new gravity and magnetic anomaly maps. The seismic data can also be correlated with the previous United States Geological Survey profile in the central Gulf of Maine.Two seismically distinct lower crustal blocks are identified: the Avalon and Sable lower crustal blocks, separated by a major north-dipping reflection zone that cuts the entire crust. The recognition of the Sable block adds a fourth block to the three already identified in the Canadian Appalachians. The Sable block is overlain by the Meguma Zone. The Avalon Zone overlies at least the northern part of the Avalon lower crustal block. Although offshore extension of geological features is not unequivocal, it appears that a north-dipping reflection zone southwest of Nova Scotia marks the site of Devonian thrusting of Avalon Zone over Meguma Zone. In the Bay of Fundy to the north, two south-dipping reflection zones are interpreted as major thrusts, possibly placing Avalon lower crust over a unit with different tectonic affinities. The Fundy Fault is a Carboniferous thrust within the Avalon block along the coast of New Brunswick; this was reactivated during Mesozoic extension as a transtensional fault. Extensional displacement farther southwest was probably accommodated along east-west-trending faults and small rift basins associated with them.

AbstractThis article integrates field, powder X-ray diffraction and microstructural data to constrain deformation mechanisms in and the rheology of granite-derived fault rocks exposed along the SE side of the crustal-scale, strike-slip Kellyland fault zone. Deformation in this area of the Kellyland fault zone localized during cooling and is marked by (1) foliated granite, (2) a ∼50 m wide band of pulverized foliated granite, (3) a ∼2.8 m wide breccia zone hosting coeval shear zones, and (4) a >100 m wide ultramylonite zone. The earliest fabric in the foliated granite is defined by elongated quartz grains, and quartz dislocation creep was the rate-controlling deformation mechanism. Seismogenic deformation initiated when recorded flow stresses reached 96–104 MPa at temperatures of 400–450 °C and is marked by coeval pulverization and formation of breccia. Interseismic viscous creep at similar flow stresses is recorded by mutual cross-cutting relationships between breccia-hosted shear zones, brittle fractures and pseudotachylyte. Field and microstructural observations indicate that breccia-hosted shear zones are low-strain equivalents of the >100 m wide ultramylonite zone, and seismogenic deformation abated as the ultramylonite formed. The rheology of ultramylonites was governed by grain-size-sensitive creep at 112–124 MPa flow stresses. Hence, from the onset of seismogenesis, the Kellyland fault zone was likely a constant-stress system wherein the rate-controlling mechanism shifted from episodic seismogenic slip and interseismic viscous creep to steady state grain-size-sensitive creep in ultramylonites derived from brittle fault rocks. Flow stresses recorded by these rocks also imply that the whole zone was relatively weak if the brittle–viscous transition and uppermost viscous zone are the strongest part of the crust.

High-resolution LiDAR (light detection and ranging) images reveal numerous NE-SW-trending geomorphic lineaments that may represent the southwest continuation of the Norumbega fault system (NFS) along a broad, 30- to 50-km-wide zone of brittle faults that continues at least 100 km across southern Maine and southeastern New Hampshire. These lineaments are characterized by linear depressions and valleys, linear drainage patterns, abrupt bends in rivers, and linear scarps. The Nonesuch River, South Portland, and Mackworth faults of the NFS appear to continue up to 100 km southwest of the Saco River along prominent but discontinuous LiDAR lineaments. Southeast-facing scarps that cross drumlins along some of the lineaments in southern Maine suggest that late Quaternary displacements have occurred along these lineaments. Several NW-SE-trending geomorphic features and geophysical lineaments near Biddeford, Maine, may represent a 30-km-long, NW-SE-trending structure that crosses part of the NFS. Brittle NWSE-trending, pre-Triassic faults in the Kittery Formation at Biddeford Pool, Maine, support this hypothesis.

Abstract Fifteen years of regional monitoring by the New England Seismic Network indicated a locally high level of seismicity near South Sebec, between the towns of Milo and Dover-Foxcroft in central Maine. Most of the events were located in a diffuse zone south of the distinctive, ENE trending Harriman Pond Fault (HPF) which is indicated by brittle deformation in outcrop and is represented as a depression in topographic maps and satellite images. A portable network consisting of both digital and analog instruments was deployed during the summers of 1989 and 1990 in order to characterize the pattern of the microearthquakes and to determine high-resolution epicenters, depths, and fault plane solutions. Seventy-three events were detected during the experiment, of which 28 could be located. Many of the events south of the fault lie along a NNW trending line which has no major expression in the surface geology. Only, a few of the events are subparallel to the HPF. The first motion data were insufficient for the determination of any fault plane solutions.

New 40Ar/39Ar mineral ages from rocks collected west of Penobscot Bay, Maine, indicate this region was regionally deformed, metamorphosed to amphibolite facies conditions, and intruded by plutons in Silurian times rather than in the Devonian as previously assumed. Disturbed hornblende age spectra, along with the presence of some Devonian felsic plutons and extensive retrograde metamorphic textures do suggest, however, that these rocks were subsequently affected by low-grade Devonian thermal events. In sharp contrast, rocks west of the Sennebec Pond thrust fault, a major tectono-stratigraphic boundary in this region, lack a significant Silurian tectono-thermal signature, and instead record the effects of intense Devonian deformation and high-grade regional metamorphism. The data suggest the two regions experienced very different pre-Devonian histories and were most likely juxtaposed by the Sennebec Pond thrust fault in latest Silurian to Early Devonian time. Rocks now exposed east of the Sennebec Pond fault probably occupied much higher structural levels during Devonian orogenesis and were not subjected to the same intense Devonian deformation and metamorphism as those rocks now found to the west of this structure. The Silurian tectonism now recognized in this region bears striking resemblance to events of similar age recorded along the northwest margin of the Avalon composite terrane throughout much of Atlantic Canada. This greatly extends the zone of Silurian orogenesis in the northern Appalachians and requires that previous models of New England middle Paleozoic tectonism be significantly revised.

Abstract Although it is widely accepted that large silicic calderas are associated with voluminous synvolcanic intrusive complexes at depth, geological evidence for caldera-forming eruptions preserved in plutonic rocks has largely been elusive. Here, we document a rare example of such evidence in the Cadillac Mountain intrusive complex, Maine (USA), where erosion has revealed a remarkable marginal “shatter zone” that records evidence for a major caldera-forming eruption. This shatter zone, up to >1 km wide, is bounded by a steep ring fault at its outer margin, which grades inward into Cadillac Mountain granite. Its outer margins are characterized by intensely brecciated and deformed country rock injected by felsite veins, reflecting explosive fragmentation associated with eruptive decompression. This marginal facies grades inward to a chaotic mélange of variably rounded and remelted country rock blocks in granitic matrix, reflecting debris eroded from ring fault conduit walls and milled in an eruptive jet before collapsing onto crystal mush. Further inward, blocks up to 80 m in size were stoped from the collapsing chamber roof and settled onto strong mush. Textural and chemical variations in the shatter zone matrix reveal syneruptive ascent of distinct silicic and more mafic magma from depth, which was likely drawn through the highly permeable shatter zone toward areas of low pressure beneath active vents. The Cadillac Mountain shatter zone provides clear evidence for a major eruption preserved in the plutonic record and supports the origin of some granites as the cumulate roots of large silicic volcanic systems.

The Avalon Peninsula, Newfoundland, Canada, defined as the type zone of Avalonia is believed to have been impacted by several orogenetic and deformation events since the Neoproterozoic. Previous studies determined the lowest degree of metamorphism reached in the successions was of the prehnite-pumpellyite or greenschist facies. We sampled and measured thirteen clastic sedimentary sections ranging from the late Ediacaran to the Early Ordovician and analysed the illite “crystallinity” of 331 samples using the Kübler index. Our results show diagenetic zones occur related to lithology, age and burial depth, respectively, and regional setting. Samples adjacent to the fault zones bounding the Holyrood Horst experienced among the highest degree of metamorphism (anchizone) in the study area. The lowest degree of thermal alteration occurs in the high stratigraphic sections at the centre of the horst structure where shallow diagenetic conditions are preserved. Fault zones, most probably active during the Acadian Orogeny, may have served as potential paths for hot fluids in bounding areas of the horst, whereas the centre of the horst remained almost unaffected by any metamorphic overprint. The thermal impact decreases from the Bonavista Peninsula to the study area from greenschist facies to anchizonal and diagenetic. The study area experienced lower metamorphic conditions than major regions of Avalonia south of the study area on the mainland of New Brunswick and Maine and eastwards in Europe. The thermal impact is in part consistent with a few other areas of Avalonia, such as the Mira terrane and the Antigonish Highlands in Nova Scotia.

High-resolution multibeam echosounder (MBES) and light detection and ranging (LiDAR) data, combined with regional gravity and aeromagnetic anomaly maps of the western Gulf of Maine, reveal numerous lineaments between central New England and the New England seamounts. Most of these lineaments crosscut the NE-SWtrending accreted terranes, suggesting that they may be surface expressions of deep basement-rooted faults that have fractured upward through the overlying accreted terranes or may have formed by the upward push of magmas produced by the New England hotspot. The 1755 Cape Ann earthquake may have occurred on a fault associated with one of these lineaments. The MBES data also reveal a NW-SE-oriented scarp just offshore from Biddeford Pool, Maine (Biddeford Pool scarp), a 60-km-long, 20-km-wide Isles of Shoals lineament zone just offshore from southeastern New Hampshire, a 50-m-long zone of mostly low-lying, WNW-ESE-trending, submerged ridge-like features and scarps east of Boston, Massachusetts, and a ~180-km-long, WNW-ESE-trending Olympus lineament zone that traverses the continental margin south of Georges Bank. Three submarine canyons are sinistrally offset ~1–1.2 km along the Thresher canyon lineament of the Olympus lineament zone.

The article reasonably shows that the uppermost layer of the Earth's crust up to 25 kilometers is seismogenic. Aim. The article provides the evidence that crustal seismicity is generated not by regional stress fields of a homogeneous shear, as it was adopted in the strategy for solving the problem of earthquake forecast, but by local fields of exponential elastic stress. Such fields arise in one or another section of a seismogenic fault due to the occurrence of a stress concentrator in this section. According to the Saint Venant principle, such a stress concentrator (an additional load in the system) generates a local stress field of an exponential form. In this field the maximum stress is localized in the areas of an increment load application (in the fault) and decreases very quickly (exponentially) on both sides of the fault. Such stress concentrators arise in those areas of a seismogenic fault, where displacements along the fault stop due to various reasons. G.A. Gamburtsev foresaw this situation and very precisely called such concentrators as “seams”. The origin of a local stress field at the place, where a seam appears, is caused by the following fact: the power impulse generated by the seam is small compared to the linear momentum of the entire system of blocks of the considered fault and, therefore, it will stop the displacement of blocks only within the seam; but the displacements of blocks outside the seam will continue in the same mode. One can single out the following reasons causing stress concentrators in the fault: variations in different stress fields, changing the value of the friction coefficient in the fault; variations in fluid processes; the influence of temperature and pressure; mechanical “hooks” of blocks due to irregularities of their contacting surfaces, etc. Methods. The fact of the existence of the considered local stress fields is confirmed by geodetic studies, i.e. the results of repeated geodetic measurements in the epicentral zones of strong earthquakes. Results.These results allow drawing the following conclusions: 1) the sign of the preparation of a crustal earthquake source was reliably determined. This sign means the increasing deformation of the elastic bending of rocks in the source in the course of time; 2) from the standpoint of solving the problem of earthquake forecast, the main and decisive result of these studies is that the deformation processes occurring in the impending source also capture the Earth's surface, because this is precisely what opens up great opportunities in solving this problem; 3) with the help of special geodetic systems (forecast profiles), one can detect the places of the impending earthquake source preparation, i.e. make an accurate forecast of the site of a future earthquake; 4) since the energy of the earthquake source is functionally related to its size, one can realize the correct prediction of the maximum possible intensity of the future earthquake by determining the length of the seismogenic fault section, elastically deformed by the preparation of the earthquake using the forecast profiles В статье обоснованно показано, что сейсмогенным является самый верхний слой земной коры мощностью до 25 километров. Цель работы. В статье приведены доказательства того, что коровая сейсмичность порождается вовсе не региональными полями напряжений однородного сдвига, как это было принято в стратегии решения проблемы прогноза землетрясений, а локальными полями упругих напряжений экспоненциального вида. Такие поля возникают в том или ином участке сейсмогенного разлома из-за появления на этом участке концентратора напряжений. Согласно принципу Сен-Венана такой концентратор напряжений (дополнительная нагрузка в системе) порождает локальное поле напряжений экспоненциального вида. Максимальная величина напряжения в этом поле расположена в месте приложения дополнительной нагрузки (в разломе) и очень быстро (экспоненциально) убывает в обе стороны от разлома. Такие концентраторы напряжений возникают на тех участках сейсмогенного разлома, на которых в силу тех или иных причин прекращаются смещения по разлому. Г.А. Гамбурцев провидчески предвидел данную ситуацию и очень метко такие концентраторы назвал «спайками»». Возникновение локального поля напряжений в месте появления спайки обусловлено тем, что импульс силы, порождаемый спайкой мал по сравнению с количеством движения всей системы блоков рассматриваемого разлома и, следовательно, он остановит смещение блоков лишь в пределах спайки, но смещения блоков вне спайки будут продолжаться в прежнем режиме. Среди причин, порождающих концентраторы напряжений в разломе можно назвать следующие: вариации различных полей напряжений, изменяющие величину коэффициента трения в разломе; влияние температуры и давления; вариации флюидных процессов; механические «зацепы» блоков из-за неровностей их соприкасающихся поверхностей и др. Методы исследования. Факт существования рассматриваемых локальных полей напряжений подтвержден геодезическими исследованиями – результатами повторных геодезических измерений в эпицентральных зонах сильных землетрясений. Результаты работы. Эти результаты позволяют сделать следующие выводы: 1) достоверно определен признак подготовки очага корового землетрясения, которым является нарастающая во времени деформация упругого изгиба горных пород в его очаге; 2) с позиций решения проблемы прогноза землетрясений главным и определяющим результатом этих исследований является то, что происходящие в готовящемся очаге деформационные процессы захватывают и земную поверхность, ибо именно это открывает большие возможности в решении этой проблемы; 3) с помощью специальных геодезических систем (прогнозных профилей) можно обнаруживать места подготовки очагов готовящихся землетрясений, т.е. осуществлять точный прогноз места будущего землетрясения; 4) так как энергия очага землетрясения функционально связана с его размерами, то определив с помощью прогнозных профилей длину участка сейсмогенного разлома, упруго деформированного подготовкой землетрясения, можно осуществить и точный прогноз максимально возможной силы будущего землетрясения

De nos jours l’utilisation intensive et abusive des ressources et le rejet des déchets dans l’environnement continuent à détériorer notre milieu. Cette situation n’est pas sans effet néfaste sur la santé humaine, l’économie, la production alimentaire, le tourisme et l’écologie. Chaque jour la pollution de notre environnement augmente, la santé humaine est de plus en plus mise en danger, mais nous nous n’en préoccupons pas comme il faut. L’étude porte sur l’analyse du rôle de la Coopérative ‘‘Isuku iwacu’’ de la Zone Kinama dans la lutte contre l’insalubrité au sein des communautés locales de la Mairie de Bujumbura. Mais alors, quelles sont les causes de l’insalubrité au sein des communautés locales en zone Kinama? Et quelles sont les conséquences de l’insalubrité sur la santé des populations de la zone Kinama? L’insalubrité dans la zone Kinama est très critique. Des immondices, caniveaux bouchés et les restaurants qui déversent des restent des épluchures au bord des rues causent l’insalubrité et la raison d’être de la coopérative « Isuku iwacu » est la lutte contre cette insalubrité. Les méthodes qualitative et quantitative ont été utilisées. 95 chefs de ménages ont été enquêtés à l’aide d’un questionnaire. Le superviseur de la coopérative « Isuku iwacu », les chefs des quartiers ainsi que le chargé d’hygiène dans la zone de Kinama ont été interviewés. Le logiciel statistique pour les sciences sociales (SPSS) version 22 nous ont guidés à obtenir les résultats. Le manque de dépotoir, la non évacuation des déchets des ménages, le refus de payer la coopérative, le manque de sensibilisation de la part des autorités et le manque des camions en bon état ont été identifiées par les enquêtés comme causes de l’insalubrité en zone Kinama, respectivement à 86,3 %, 94,7%, 82,1%, 94,7% et 76.8%. Les mauvaises odeurs, les maladies des mains salles, la dysenterie, les vers intestinaux, la malaria, la diarrhée et les maladies de la peau ont été identifiées, respectivement à 35,8%, et 98,9%, 87,4%, 81,1%, 53,7%, 88,4% et 65,3% comme étant les conséquences majeures de l’insalubrité en zone Kinama.